>> elizabeth, there's a photograph of dzhokhar tsarnaev after he was apprehended, it was from i think the bureau of alcohol, tobacco, firearms, a picture of him down, and he was being intubated, a tube being put in his mouth to help with his breathing. that would suggest that he was in bad condition there. explain to people when people say he's in serious condition but not critical condition, what exactly is the difference? >> reporter: critical condition often means someone's life is on the line, they're not really sure if he is going to survive. it sounds like they feel that he is going to survive. certainly the fact he was intubated tells us something, tells us that this is not just, you know, a small thing, but the fact that it is serious enough, critical means he is likely to survive. >> all right, elizabeth, thank you so much. with the hunt over for the suspects, one dead, one in custody, investigators are focusing on the full puzzle. they want to find out what motivated these two brothers, described by many that knew them years before as normal, but they're certainly not normal